Mechanical fuel injectors for both diesel and gasoline engines generally have various critical parts which can impede the operational performance of the injector and engine due to design precision and field service wear. Such fuel injectors are typically designed to be located and seated in a tapered hole in the center of a cylinder head. For the locomotive style fuel injector the upper external working parts of the injector are lubricated by oil splash that enters through a clearance around the metering rack. However, the lower internal working parts are lubricated and cooled by the flow of diesel fuel through the lower half of the injector.
One of the critical internal working injector components subject to wear is the plunger. The injector plunger is primarily responsible for the proper atomization of the fuel which is accomplished by the high pressure created during the downward stroke of the plunger. The downward stroke of the plunger forces the fuel past a check valve and out through spray holes in the injector tip via the connecting fuel passages. The plunger is placed in motion within the fuel injector by an engine cam either directly or indirectly acting through a rocker arm and injector follower which pushes the plunger. Rotation of the plunger is accomplished by a rack and gear system linked to the engine governor that controls the quantity of high pressure fuel injected into the combustion chamber during the cylinder's power stroke.
Typically, the injector plunger includes smooth helical ridges formed near each end of the plunger to control the opening and closing of the fuel ports within the injector's bushing in which the plunger operates. The continuous helical ridges mechanically determine the opening and closing of the supply and return ports of the injector's plunger bushing. Typically, two opposed helical shaped ridges are located on the plunger. The first opposed helical ridge controls the start of the injection event timing and the second opposed helical ridge ultimately controls the quantity of high pressure fuel delivered by ending the injection event. The timing control helix ridge closes the bushing's fuel supply port to start the fuel injection event and the fuel control helix then opens the bushing's fuel return port to end fuel injection event. As the two opposed helical ridges are machined or formed closer together, the gap between the two grows smaller and the fueling rate is increased such that the duration from the closing of the fuel supply port to the opening of the fuel return port is extended.
Fuel delivery to the cylinder's combustion chamber is regulated in part by the rotation of the plunger which regulates the duration that the supply and return fuel ports are closed during the downward stroke. As the plunger is rotated from the idling position to the full load position, the pumping stroke is lengthened and the distance between the two opposed helical ridges becomes less and the start of injection begins earlier in the combustion cycle which allows for more fuel to be injected. The various degrees of rotation correspond to a locomotive engine's throttle positions. Typically, one notch or throttle position corresponds to 25 degrees of rotation. For example, a notch setting of one on a typical diesel locomotive corresponds to 50 degrees rotation, a notch eight position corresponds to 225 degrees of rotation and at idle the degree of rotation is 25 degrees.
Typically, both the timing and fuel control helix ridges are machined into the plunger body as serpentine ridges continuously sloping up the side of the plunger. Thus, a sloping diagonal profile of the helix edge is presented and passed across the opening of the supply and return fuel ports during each injection cycle. Unfortunately, this sloping edge profile is unable to provide the precise control of the injection cycle's fueling duration event. Precision control is desirable in optimizing of the fuel injection timing to both control harmful engine emissions and to reduce fuel consumption. The manufacturing tolerances of a typical diesel engine injector plunger are such that the sloping edge profile of the continuously angled timing helix is unable to consistently and accurately close the bushing's fuel inlet port to initiate the start of injection.
Furthermore, the sloping edge profile of a continuously angled helix ridge is not able to accurately differentiate between notches due to worn mechanical fuel linkages. Each notch represents a set plunger rotation that presents a desired angle profile or position of the plunger to control or start the injection event. Worn mechanical linkages can cause the set rotation of each desired notch setting to deviate from its preset location such that the timing for the injection event is altered given that a different angle profile is presented on the plunger as it is rotated beyond or before its preset notch location.
Additionally, the continuously sloping edge profile and angled helical ridge promotes accelerated wear of the helix edge given the inherent sweeping motion of the plunger as it moves across the fuel supply inlet port opening. Pressurized fuel is forced up and over the helix edge as the edge profile is moved across the inlet port. This fuel movement is not uniform across the edge profile and is concentrated along the lowest sloping portion of the leading edge of the helix ridge. The concentrated fuel flow results in an uneven wear on the helix edge that may eventually alter the injection timing. The altered injection timing impedes the engine's performance since the start of injection is no longer optimized for a particular notch setting or performance characteristic.
A further disadvantage associated with the continuously angled helices or ridges is their inability to mechanically and accurately accommodate significant change in timing between adjacent notches. A significant change in timing between notches requires extreme changes in the continuously angled helix ridge as to make such accommodations almost impossible to accomplish.
Thus, what is needed is a method and apparatus capable of providing an optimized timing event that overcomes the varying manufacturing tolerances and inherent wear associated with mechanical injection timing.